The present invention relates to vulcanizing apparatus for vulcanizing endless rubber belts such as power transmission rubber belts.
Endless rubber belts of this type are produced by winding belt constituent members, including unvulcanized rubber sheet, canvas, cords, etc., over the outer circumference of a mold to form a cylindrical unvulcanized rubber slab, vulcanizing, cooling and removing the cylindrical rubber and slicing the slab into belts of a desired width.
One typical vulcanizing apparatus for vulcanizing an unvulcanized rubber belt form is the gasket vulcanizing apparatus, and a cross sectional view of one portion of the apparatus is shown in FIG. 6. Ring-shaped capping members 52 and 53 are fixed to both the upper and bottom ends of a mold 51 in such a way that the capping members cover both the upper and bottom ends of an unvulcanized rubber belt molding A formed over the outer circumference of the mold 51 between the members 52 and 53. Then the whole assembly is inserted into a metal sleeve 55. The metal sleeve 55 has a rubber sleeve 54 of which both the top and bottom ends are fixed to the inner circumference of the metal sleeve 55. Pressurized steam is introduced through a pipe into the space between the rubber sleeve 54 and the metal sleeve 55 to apply pressure on the molding A and heat it to effect vulcanization. The above-mentioned vulcanizing apparatus is placed inside a sealable vulcanizing vessel (not illustrated) and the pressurized steam is introduced inside the vulcanizing vessel. An apparatus similar to that described above is disclosed, for example, in U.S. Pat. No. 4,095,480.
The above-mentioned conventional vulcanizing apparatus, however, has room for further improvements on the following points:
(1) In the vulcanizing operation, capping members 52 and 53 must be selected according to the size of the mold 51 and the thickness of the unvulcanized rubber belt molding A. Replacement of the capping members for each size takes time and labor. PA1 (2) The second point relates to the vulcanized product. The capping members 52 and 53 are made of metal, and these members are quickly heated up upon the introduction of the pressurized steam. As a result, the upper and lower portions X (see FIG. 5 (b)) of the unvulcanized rubber belt molding A have a greater vulcanizing speed relative to other portions (Y and Z), as shown by the curve X' in FIG. 5 (a) which indicates the states of vulcanization, and become overcured. The upper and lower portions X of the unvulcanized rubber belt molding A will shrink and prevent the gas released by the rubber belt molding A from escaping. Then the gas will remain in the form of bubbles which in turn may produce pin holes or deteriorate the quality of the rubber belt.
Moreover, there is a gap between the mold 51 and the capping members 52 and 53. During the vulcanization a part of the unvulcanized rubber belt molding A will melt and flow into the gap. As a result, the top and bottom portions of the rubber belt must be wasted since the form of these portions is irregular. The yield, therefore, is reduced.